@article {80093, title = {Microtubules provide guidance cues for myofibril and sarcomere assembly and growth.}, journal = {Dev Dyn}, volume = {250}, year = {2021}, month = {07/2020}, pages = {60-73}, abstract = {

BACKGROUND: Muscle myofibrils and sarcomeres present exceptional examples of highly ordered cytoskeletal filament arrays, whose distinct spatial organization is an essential aspect of muscle cell functionality. We utilized ultra-structural analysis to investigate the assembly of myofibrils and sarcomeres within developing myotubes of the indirect flight musculature of Drosophila.

RESULTS: A temporal sequence composed of three major processes was identified: subdivision of the unorganized cytoplasm of nascent, multi-nucleated myotubes into distinct organelle-rich and filament-rich domains; initial organization of the filament-rich domains into myofibrils harboring nascent sarcomeric units; and finally, maturation of the highly-ordered pattern of sarcomeric thick (myosin-based) and thin (microfilament-based) filament arrays in parallel to myofibril radial growth. Significantly, organized microtubule arrays were present throughout these stages and exhibited dynamic changes in their spatial patterns consistent with instructive roles. Genetic manipulations confirm these notions, and imply specific and critical guidance activities of the microtubule-based cytoskeleton, as well as structural interdependence between the myosin- and actin-based filament arrays.

CONCLUSIONS: Our observations highlight a surprisingly significant, behind-the-scenes role for microtubules in establishment of myofibril and sarcomere spatial patterns and size, and provide a detailed account of the interplay between major cytoskeletal elements in generating these essential contractile myogenic units. This article is protected by copyright. All rights reserved.

}, issn = {1097-0177}, doi = {10.1002/dvdy.227}, author = {Dhanyasi, Nagaraju and VijayRaghavan, K and Shilo, Ben-Zion and Schejter, Eyal D} } @article {1044, title = {Surface apposition and multiple cell contacts promote myoblast fusion in Drosophila flight muscles.}, journal = {J Cell Biol}, volume = {211}, year = {2015}, month = {2015 Oct 12}, pages = {191-203}, abstract = {

Fusion of individual myoblasts to form multinucleated myofibers constitutes a widely conserved program for growth of the somatic musculature. We have used electron microscopy methods to study this key form of cell-cell fusion during development of the indirect flight muscles (IFMs) of Drosophila melanogaster. We find that IFM myoblast-myotube fusion proceeds in a stepwise fashion and is governed by apparent cross talk between transmembrane and cytoskeletal elements. Our analysis suggests that cell adhesion is necessary for bringing myoblasts to within a minimal distance from the myotubes. The branched actin polymerization machinery acts subsequently to promote tight apposition between the surfaces of the two cell types and formation of multiple sites of cell-cell contact, giving rise to nascent fusion pores whose expansion establishes full cytoplasmic continuity. Given the conserved features of IFM myogenesis, this sequence of cell interactions and membrane events and the mechanistic significance of cell adhesion elements and the actin-based cytoskeleton are likely to represent general principles of the myoblast fusion process.

}, issn = {1540-8140}, doi = {10.1083/jcb.201503005}, author = {Dhanyasi, Nagaraju and Segal, Dagan and Shimoni, Eyal and Shinder, Vera and Shilo, Ben-Zion and VijayRaghavan, K and Schejter, Eyal D} }